Thirty patients undergoing transurethral resection of the prostate using ethanol-tagged irrigating fluid were investigated in order to study the effects of a breach in the prostatic capsule. Measurements were made of end-tidal ethanol (ET-ethanol) in the expired air, serum glycine and sodium, haemoglobin, blood loss and volumetric determination of irrigating fluid absorption. Perforation of the prostatic capsule occurred in 13 patients (Group P), with 17 judged to have no perforation (Group NP). In all Group NP patients the ET-ethanol remained below 0.05/1000, serum sodium decreased by < or = 3 mmol/l and serum glycine remained < 1.5 mmol/l. ET-ethanol was significantly increased in Group P, rising to between 0.1 and 0.45/1000 in 5 patients, 3 of whom showed a reduction in serum sodium > 5 mmol/l. Five patients in Group P demonstrated significantly raised serum glycine concentrations up to 15 mmol/l. These findings suggest that perforation of the prostatic capsule may lead to rapid absorption of irrigating fluid, and that ET-ethanol monitoring is a useful method of detecting this quickly.